This is the sixth in a series of posts, collected here, on Thomas Nagel's Mind and Cosmos (Oxford 2012). In my last post I suggested that Nagel needs a principle of plenitude in order to explain the actual existence, as opposed to the mere possibility, of rational organisms. But maybe not, maybe teleology will turn the trick for him. So we need to see what he says about teleology.
Nagel distinguishes "constitutive" from "historical" questions. What is reason? is an example of the former; How did reason arise? of the latter. Now one might wonder whether reason is the sort of thing that could arise. I am tempted to say that reason could no more arise than truth could arise, but then I'm a theist. Nagel, however, must hold that reason arises given his monism. As a monist, he maintains that there is exactly one world, this natural world.
Off the top of my head, I suggest we have at least six options concerning the nature and origin of reason.
A. Interventionist Theism. Reason didn't arise, but always existed. God is its prime instance and source. Reason in us did not arise or emerge from irrational or pre-rational elements but was implanted by God in us. It is part of what makes us of higher origin, an image and likeness of God.
B. Noninterventionist Deism. Reason didn't arise, but always existed. God is its prime instance and source. But God did not infuse or implant reason in certain animals at any point in the evolutionary process; what he did is rig up the world in such a way that rational animals would eventually emerge. Nagel mentions something like this possibility on p. 95.
C. Transcendental Subjectivism. Reason didn't arise, but neither is God its prime instance and source. Reaon is an a priori structure of our subjectivity, a transcendental presupposition without which we cannot carry out our cognitive operations. A view like this could be read out of Kant. A transcendental idealism as opposed to the Hegelian objective idealism that Nagel supports. (17)
D. Reason is a fluke. Reason arose, but it was a cosmic accident. That there are rational beings is simply a brute fact. Nagel rightly rejects this view.
E. Materialist evolutionary naturalism operating by "directionless physical law." (p. 91)
F. Nature-immanent non-intentional teleology.
Nagel rejects all of these options except the last. Unfortunately, Nagel's proposal is so sketchy it is hard to evaluate. To get a handle on it we need to study Nagel's final chapter on value in a separate post. According to natural teleology, the world has an in-built propensity to give rise to beings for whom there is a difference between what is good for them and what is bad for them. There is no agent who intends that such beings should arise; there is just this tendency toward them in nature below the level of mind. And so the explanation of the existence of such beings is not merely causal but teleological: there is is a sort of axiological requiredness in rerum natura that pulls as it were from the future these beings into existence. (See p. 121) This is my way of putting it.